Electrical shunt



Jam- 26, 1943. M. GILSON ET AL 2, 3

ELECTRICAL SHUNT Filed .July 1'7, 1940 Insulation INVENTORS RobemMfiL'lson and Ralp uerlzalz,JP. 4; BY I THEIR F "ATTORNEY Patented Jan. 26, 1943 ELECTRICAL SHUNT Robert M. Gilson and Ralph Overholt, J12, Pittsburgh, Pa., assignors to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application July 17, 1940, Serial No. 345,960

4 Claims.

Our invention relates to electrical shunts and more particularly to a combination of an electrical shunt and a lightning arrester in which the resistance element is readily removable by hand and provides protection not only against lightning discharges but also against excessive voltages such as may be below the sparking voltage of the arrester.

One object of our invention-is to provide a simple, effective and inexpensive mounting for the resistance element of the combined shunt and lightning arrester. Another object of our invention is to provide a mounting assembly such that each part in one portion of the assembly is interchangeable with the corresponding part in another portion of the assembly, and the assembly as a whole permits manual removal and replacement of the resistance element easily without danger of breakage or damage to this element. our invention will be apparent from the description which follows.

We accomplish the foregoing objects by using a resistance element having a negative resistance-voltage characteristic in parallel with? a spark gap and by using identical top and bottom clamping members for the resistance element, with identical means at each side of the element for fastening the clamping members together firmly as a unit, the parts being so designed and arranged so as to permit springing by hand into a firmly locked position.

In the accompanying drawing, Fig. 1 is an elevation showing one form of electrical shunt embodying our invention. show certain details of the shunt shown in Fig. 1. Fig. 4 is an elevation showing a modified form of the apparatus of Fig. 1, also embodying our invention.

Similar reference characters refer to similar parts in each of the several views.

Referring to Fig. 1 of the drawing showing an elevation of the assembled shunt, the insulating base I having the raised portions 3 and the terminal posts 2 comprise a terminal block such as the standard terminal block adopted by the American Association of Railroads. The terminal posts of this block with their usual complement of Washers and clamping nuts provide the elec trical connections as well as the mechanical support for the shunt assembly.

The resistance element of the shunt is preferably in the form of a disc or button 4 and may be composed of any suitable resistance material which has the desired resistance-voltage charac- Other objects, purposes, and features of Figs. 2, 2a, 3 and 3a teristic from the standpoint of the device to be protected. We have found that for protecting devices such as copper oxide rectifiers, the material commercially known as thyrite is well suited because the resistance at normal working voltage is sufficiently high to be unobjectionable and becomes sufiiciently low to provide eliective protection when the voltage exceeds a safe value. Any other resistance element having the proper negative resistance-voltage characteristics can, of course, be used.

The resistance element 4 is held in place by means of two cup-shaped washers or discs 5a and 5b which in turn are riveted or fastened to the supporting or clamping members to and 671. As shown, these discs are riveted to the clamping members by means of the rivets 1. Preferably, the discs 5a and 5b are each provided with a sawtooth edge for facilitating a discharge between them should the voltage reach extreme Values.

The clamping members or spring plates 6a and 6b, twoviews of which are shown in Figs. 2 and 2a, are made of suitable material such as hard brass or phosphor bronze which has the necessary rigidity and yet is sufficiently flexible to permit thetwo members to be manually compressed and locked in place by means of the double-headed insulating pins 8a and 81), one of which is shown in Figs. 3 and 3a. The hole 9 in the top clamping member (as seen in Fig. 2) is sufficiently large to permit the head of the insulating pin 8a to be passed therethrough whereas the recesses I0 and l l are just suflicient to provide clearance for the shank of this pin. The inner surfaces of the heads of each pin are beveled to permit seating in the beveled recesses l2 and [3. The spring plates Ea. and 6b ,aresprung slightly beyond the flat position (as seen in Fig. 2a) in the punching operation so that these plates will exert pressure tending to keep the assembly firmly locked, once the pins are in place. It will be noted that the insulating pins Ba. and 8b are inserted into the recess l0 of the respective spring plate before the cupped washers 5a and 5b are riveted in place so that. the pins are not removable and consequently cannot become lost.

It will also be noted that the washers 5a. and 5b are so shaped as to ride free of the disc 4 at the edges thereof and at the center where clearance for the rivet l is required. One reason for this construction is that the disc 4 in commercial form has a metallic contact layer formed on its top and bottom surface but this layer cannot, in practice, be carried to the very edge of the disc. Consequently, it is necessary to avoid contact near the edge of the disc as such contact might be beyond the metallic layer and cause high resistance by preventing proper contact with the formed surface.

Another reason for shaping the washers 5a and 5b as shown is that this construction provides a not too great area of contact to resist slight turning of the washer 5a when the parts 5a and 6a are riveted together. It is, of course, desirable that the points of the saw-teeth on the two washers be opposite one another as the voltage at which a discharge will pass between the teeth is determined by their separation or air gap. Uniformity in this air gap can be obtained by rotating one washer slightly until the teeth thereof register with the teeth of the other washer. In order to take care of manufacturing variations and tolerance in the thickness of the discs 4 and other parts, circular shims or spacers (not shown) can be introduced between the disc 4 and either washer, or both, to provide the necessary discharge gap.

It will be further noted that the washers 5a and 5b establish contact over an appreciable area of the disc 4 and that desirable heat conducting junctions exist between this disc and the washer 5a, spring plate 6a and the binding post 2. This intimate metallic contact aids in the rapid flow of heat so as to increase its dissipation and so increase the safety, reliability and life of the protective unit.

After the insulating pins are inserted in the spring plates and the washers are riveted in place, the shunt may be assembled. This is done by placing the disc 4 between the two cupped washers as shown in Fig. 1 and compressing the free end of each spring plate until the respective insulating pin which now rests in recess 12 of the upper spring plate 6a passes through the slot l I in the lower spring plate 6b and is seated in recess l3. This operation is easily performed by hand before the shunt assembly is mounted on the terminal block I and entails no danger of breakage or damage to disc 4 as only a gentle compressive force is applied thereto. The shunt assembly can now be slipped over the binding posts 2 and secured firmly in place on the terminal block. The spring plates are sufficiently thin as to require no increase of length in the binding posts of the standard terminal block so that the assembly requires a minimum of special parts.

Should it be desired to replace the disc 4, this can be done simply by reversing the assembly procedure described above. shunt is removed from the terminal block, slight compression of the spring plates enables the free ends of the insulating pins to be pushed out of their respective slots I! so that the disc 4 becomes free. The new disc is then looked firmly in place, as before.

In the modified form of the invention shown in Fig. 4, the two clamping members 6c and 6d are held firml together by means of the rectangular insulating sleeves 14a and [4b. In assembling. the members 60 and 6d are pressed together until the insulating sleeves will pass over the free end of the respective clamping member, thus providing an assembly which is mechanically rigid but which permits removal or replacement of the resistance element to be readily made.

The clamping members 6a and 6b, retaining discs 5a and 5b, and pins 8a and 8b of Fig. l are duplicate or identical parts. The same is also true of the corresponding parts of Fig. 4, so that That is, when the there is obtained economy of parts in manufacture.

It will be apparent from the foregoing description that we have provided a simple and effective form of combined electrical shunt and lightning arrester employing a minimum number of parts and permitting removal or replacement of the resistance element to be made simply and easily. The resistance element can be selected such as to provide shunt protection against voltages which may be well below the sparking voltage of the shunt when acting as an arrester so that at high voltages, th apparatus embodying our invention provides two protective paths in parallel, one through the spark gap and another through the resistance element. Since the apparatus is of small size and can be mounted on the usual ter minal block, no additional housing space is re quired by the assembly.

Although we have herein shown and described only two forms of an electrical shunt embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

l. A mounting for an electrical resistance unit comprising in combination, a pair of spaced spring clamping plates for clamping the unit therebetween and for providing a conducting path with said unit, said clamping plates being provided with a plurality of opposing slots in alignment with each other, one of each slot pair being closed and the slot aligned therewith being open, and a shouldered insulating pin for each said slot pair, said pin engaging one clamping plate at said closed slot and insertable by means of finger pressure into said open slot of the pair against the spring pressure of said clamping plates, whereby the shoulders of said insulating pins trap said spring pressure against said resistance unit to hold said unit firmly in place and render said unit readily removable by hand.

2. A mounting for an electrical resistance unit comprising in combination, a pair of spaced spring clamping plates for clamping the unit therebetween and for providing a conducting path with said unit, said clamping plates being provided with a plurality of opposing slots in alignment with each other, one of each slot pair being closed and the slot aligned therewith being open. a conducting retaining member fastened to each clamping plate for retaining said unit in position against lateral displacement, and a shouldered insulating pin for each said slot pair, the closed slot of each pair having an enlarged portion and a restricted portion, said pin being insertable through said enlarged portion into said restricted portion for locking against removal by said retaining member, the shoulder at one end of said pin engaging one clamping plate at said closed slot, said pin being insertable by means of finger pressure into said open slot of the pair against the spring pressure of said clamping plates, whereby the shoulder at the other end of said pin engages said other clamping plate and traps said spring pressure against said resistance unit to hold said unit firmly in place and render said unit readily removable by hand.

3. A mounting for an electrical resistance unit comprising in combination, a pair of spaced spring clamping plates for clamping the unit therebetween and for providing a conducting path with said unit, and two insulating locking members one at each side of said unit, said plates having their free ends in alignment with one another, said insulating members having a pair of confronting inner surfaces for engagement with the outer surfaces of said clamping plates, said insulating members being movable by means of finger pressure into locking position, whereby said inner surfaces engage said free ends and trap the spring pressure of said clamping plates against said resistance unit to hold said unit firmly in place and render said unit readily removable by hand.

4. A mounting for an electrical resistance unit comprising in combination, a pair of spaced spring clamping plates for clamping the unit therebetween and for providing a conducting path with said unit, and two insulating sleeves one at each side of said unit, said plates having their free ends in alignment with one another for engagement by the confronting inner surfaces of said insulating sleeves, said sleeves being slidable by means of finger pressure over said free ends against the spring pressure of said clamping plates, whereby said sleeves trap said spring pres sure against said resistance unit to hold said unit firmly in place and render said unit readily re movable by hand.

ROBERT M. G-ILSON.

RALPH OVERHOLT, JR. 

